The newer MDCT scanners have shorter scan times it was necessary to re-evaluate the injection protocols for CTA. Bolus tracking is a method that individualizes the timing of contrast media (CM) delivery to a region of interest (ROI). An injection of CM is tracked or observed until it reaches the desired Hounsfield Units (HU) threshold for the ROI. When that threshold is met wait a few seconds and then scan to obtain the optimal image enhancement.
This method of imaging is used primarily to produce images of arteries, such as the aorta, pulmonary artery, cerebral and carotid arteries. The image shown below illustrates this technique on a sagittal MPR (multiplanar reformat). The image is demonstrating the blood flow through an abdominal aortic aneurysm or AAA. The bright white on the image is the contrast. You can see the lumen of the aorta in which the contrast is contained, surrounded by a grey "sack", which is the aneurysm. Images acquired from a bolus track, can be manipulated into a MIP (maximum intensity projection) or a volume rendered image.
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